Such a method and apparatus are well known, e.g. from U.S. Pat. No. 5,852,646. In said document a 3-dimensional volume of an object can be derived from a number of 2-dimensional computer tomograms by means of a CT-apparatus. The obtained 3-dimensional volume is related to the X-ray images; an association of corresponding projection images of this volume with the X-ray images results in a series of superposition images, which reproduces the two anatomic structures in geometrically correct association. In such a way information, inherent to CT-measuring methods, e.g. information about tumors, is combined with typically X-ray information, e.g. information about blood vessels.
In general, a similar set of X-ray images can be obtained by using an X-ray apparatus with a rotatable source around its isocenter. To enable such rotations conventional X-ray apparata are equipped with a C-arm, the technical details of such a construction falling within the scope of general knowledge of a person skilled in the art of X-ray imaging. When a method as described in the opening paragraph is applied to a moving object, such as a beating heart or more specifically the coronary vascular system of a beating heart of a human or animal, filled with a contrast medium, it is often standard practice to use a C-arm rotation speed in the X-ray apparatus of about 30°/s (degrees per second) or a scan duration or run length of about 6 s. During each run images are obtained for only certain angle areas. To cover the whole angle area of 180° several runs are necessary, the starting angle of each run relative to the cardiac cycle being adjusted by triggering the start of the run with a certain phase within the cardiac cycle. The images obtained can be used for a reconstruction of a 3-dimensional volume. During this process a movement of the heart contributes to artefacts in the reconstructed image. With a heart rate of 60 beats per minute and a framerate of for example 25 images per second during a scan movement over 180°, during each hart beat 25 images are obtained and with 5 images in each specific phase of the cardiac cycle, 6 times 5 images are obtained, or, in other words, during each scan 5 times 6 corresponding X-ray images of a quasi-stationary heart can be obtained, which can be used for reconstruction of a 3-dimensional volume. Problems of the known method are the necessity to correlate the different sub-runs in order to produce the 180° run as well as poor quality of the reconstructed image.